Added some documentation about the test option

addons/storyshots/README.md

@@ -100,3 +100,19 @@ initStoryshots({
 ### `framework`
 
 If you are running tests from outside of your app's directory, storyshot's detection of which framework you are using may fail. Pass `"react"` or `"react-native"` to short-circuit this.
+
+### `test`
+
+Run a custom test function for each story, rather than the default (a vanilla snapshot test). See the exports section below for more details.
+
+## Exports
+
+Apart from the default export (`initStoryshots`), Storyshots also exports some named test functions (see the `test` option above):
+
+### `snapshot`
+
+The default, render the story as normal and take a Jest snapshot.
+
+### `renderOnly`
+
+Just render the story, don't check the output at all (useful if you just want to ensure it doesn't error).